Epidermal Cell Death in Rice Is Regulated by Ethylene, Gibberellin, and Abscisic Acid

Abstract

Programmed cell death (PCD) of epidermal cells that cover adventitious root primordia in deepwater rice (Oryza sativa) is induced by submergence. Early suicide of epidermal cells may prevent injury to the growing root that emerges under flooding conditions. Induction of PCD is dependent on ethylene signaling and is further promoted by gibberellin (GA). Ethylene and GA act in a synergistic manner, indicating converging signaling pathways. Treatment of plants with GA alone did not promote PCD. Treatment with the GA biosynthesis inhibitor paclobutrazol resulted in increased PCD in response to ethylene and GA presumably due to an increased sensitivity of epidermal cells to GA. Abscisic acid (ABA) was shown to efficiently delay ethylene-induced as well as GA-promoted cell death. The results point to ethylene signaling as a target of ABA inhibition of PCD. Accumulation of ethylene and GA and a decreased ABA level in the rice internode thus favor induction of epidermal cell death and ensure that PCD is initiated as an early response that precedes adventitious root growth.

Emerging Roots Alter Epidermal Cell Fate through Mechanical and Reactive Oxygen Species Signaling

“…A dose-response analysis of ethephon-induced cell death at the third node of wild-type rice cultivar Zhonghua 11 showed that epidermal cell death was induced in a dose-dependent manner by ethephon (see Supplemental Table 1 online) as was shown previously for other rice cultivars (Mergemann and Sauter, 2000;Steffens and Sauter, 2005). Treatment with 15 mM of ethephon resulted in 8.0 and 19.0% cell death after 22 h and 48 h, respectively, as compared with 1.0 and 10.9% in controls.…”

A Co-Opted Hormonal Cascade Activates Dormant Adventitious Root Primordia upon Flooding in Solanum dulcamara

“…The negative effect of ethylene on ABA accumulation in Arabidopsis seedlings was accompanied by lower NCED expression and higher ABA 89-hydroxylase gene expression, as in the signaling cascade described here (Cheng et al, 2009). In rice, ABA treatment hampers flooding-induced AR emergence by preventing epidermal cell death (Steffens and Sauter, 2005), but it has not been reported whether ABA levels actually go down at the site of the preformed AR primordia and whether this is sufficient to mimic the flooding and ethylene responses. ABA also has a prominent role in dormancy initiation and maintenance in seeds and vegetative organ buds (Arend et al, 2009;Nambara et al, 2010;Reddy et al, 2013).…”

Programmed Cell Death as a Response to High Light, UV and Drought Stress in Plants

“…Such counteracting role of these hormones relates to their influence on the ROS-scavenging enzymes expression [49]. ABA has been also shown to delay ET-and GA-induced cell death in rice epidermal cells [50]. All these interactions between phytohormones and ROS indicate the complexity of PCD regulation.…”